Ion-Radical Chemistry in a Controlled Experiment

在这项由化学系化学结构、动力学和机制(CSDM-A)计划资助的项目中，科罗拉多大学博尔德分校的Heather Lewandowski教授和她的研究小组正在使用激光冷却和陷阱技术来研究分子离子和中性自由基分子之间的化学反应。分子离子是缺少电子(因此带正电荷)或有额外电子(使它们带负电荷)的分子。中性自由基分子不带电荷，但含有未配对的电子。分子上的电荷和它是否有未成对的电子对分子的化学反应活性有很大的影响。莱万多夫斯基实验室开发了激光冷却和离子捕获仪器，可以精确控制离子和自由基碰撞的速度和能量。控制碰撞的能力使研究小组能够评估电荷和未配对电子如何影响化学反应的速度和结果。这项工作架起了分子物理、物理化学和天体化学之间的桥梁。从事这一项目的学生在先进的激光光学技术和计算化学方面获得了宝贵的知识和技能。本项目专注于确定被困在射频陷阱中的交感冷却分子离子与利用时变非均匀电场减速的中性自由基分子束之间的反应速率和反应机理。通常，中性分子包括OH、CH和NH3，而离子物种是不同的，以研究与天体物理和大气相关的大范围反应。在反应实验发生后，陷阱中的所有离子，包括所有产物离子，都被喷射到飞行时间质谱仪中，以进行质量与电荷的识别。通过改变反应时间，确定了反应速度。利用势能面的高水平理论计算对实验数据进行了解释。这项工作的更广泛的影响包括培训学生使用分子物理和物理化学技术和观点进行跨学科研究。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

In this project funded by the Chemical Structure, Dynamics, and Mechanisms (CSDM-A) Program of the Chemistry Division, Professor Heather Lewandowski and her research group at the University of Colorado at Boulder is using laser cooling and trapping techniques to study chemical reactions between molecular ions and neutral free-radical molecules. Molecular ions are molecules that are either missing electrons (and therefore are positively charged) or have extra electrons (making them negatively charged). Neutral free-radical molecules are not charged, but have electrons that are unpaired. The charge on a molecule and whether or not it has unpaired electrons greatly influences the chemical reactivity of the molecule. The Lewandowski laboratory has developed laser cooling and ion trapping instruments that can precisely control the speed and energy with which the ions and radicals collide. The ability to control collisions allows the team to evaluate how charge and unpaired electrons affect the speeds and outcomes of chemical reactions. This work bridges the communities of molecular physics, physical chemistry, and astrochemistry. The students working on this project gain valuable knowledge and skills in advanced laser optical techniques and computational chemistry.This project focuses on determining reaction rates and mechanisms for reactions between sympathetically cooled molecular ions trapped in a radio-frequency trap and a neutral free radical molecular beam decelerated using time-varying inhomogeneous electric fields. Typically, neutral molecules include OH, CH and NH3, while the ion species are varied to study a large range of astrophysically- and atmospherically-relevant reactions. After a reaction experiment has taken place, all of the ions in the trap, including all product ions, are ejected into a time-of-flight mass spectrometer for mass-to-charge identification. By varying the reaction time, the reaction rate is determined. The experimental data are interpreted with the help of high-level theoretical calculations of the potential energy surface. The broader impacts of this work include training of students in interdisciplinary research using both molecular physics and physical chemistry techniques and perspectives.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.